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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.signal_set.async_wait"></a><a class="link" href="async_wait.html" title="signal_set::async_wait">signal_set::async_wait</a>
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<p>
          <a class="indexterm" name="asio.indexterm.signal_set.async_wait"></a> 
Start an asynchronous
          operation to wait for a signal to be delivered.
        </p>
<pre class="programlisting">template&lt;
    typename <a class="link" href="../SignalHandler.html" title="Signal handler requirements">SignalHandler</a>&gt;
<a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_wait(
    SignalHandler &amp;&amp; handler);
</pre>
<p>
          This function may be used to initiate an asynchronous wait against the
          signal set. It always returns immediately.
        </p>
<p>
          For each call to <code class="computeroutput">async_wait()</code>, the supplied handler will be
          called exactly once. The handler will be called when:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
              One of the registered signals in the signal set occurs; or
            </li>
<li class="listitem">
              The signal set was cancelled, in which case the handler is passed the
              error code <code class="computeroutput">asio::error::operation_aborted</code>.
            </li>
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<h6>
<a name="asio.reference.signal_set.async_wait.h0"></a>
          <span><a name="asio.reference.signal_set.async_wait.parameters"></a></span><a class="link" href="async_wait.html#asio.reference.signal_set.async_wait.parameters">Parameters</a>
        </h6>
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<p class="title"><b></b></p>
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<dt><span class="term">handler</span></dt>
<dd>
<p>
                The handler to be called when the signal occurs. Copies will be made
                of the handler as required. The function signature of the handler
                must be:
</p>
<pre class="programlisting">void handler(
  const asio::error_code&amp; error, // Result of operation.
  int signal_number // Indicates which signal occurred.
);
</pre>
<p>
                Regardless of whether the asynchronous operation completes immediately
                or not, the handler will not be invoked from within this function.
                Invocation of the handler will be performed in a manner equivalent
                to using <code class="computeroutput">asio::io_context::post()</code>.
              </p>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2018 Christopher M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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